In the past, blood pumps have been used successfully to treat patients with late stage congestive heart disease or failure. Commonly, pulsatile blood pumps or continuous flow rotary blood pumps have been connected in parallel to a patient's heart to supplement or assist their heart in pumping blood through the patient's circulatory system. These types of blood pump are been commonly called left ventricular assist devices (LVADs) because they are generally connected between the left ventricle of the patient's heart and the aorta to offload the heart.
A preferred example of an implantable rotary blood pump is described in U.S. Pat. No. 6,227,797 (Watterson et al). This pump is a continuous flow blood pump which includes a hydrodynamically suspended impeller that rotates to impart a centrifugal force on the blood in the pumping chamber. The blood is propelled to the rest of the circulatory system. The impeller described within this specification is generally shaft-less and this feature may significantly reduce the areas or regions stagnation for the blood travelling through the pump. U.S. Pat. No. 6,227,797 describes a blood pump suitable for implantation within the body of the patient.
The concept of an implantable ultrasonic sensor for detecting blood flow is detailed within U.S. Pat. No. 5,865,749 (Doten et al). This disclosure describes an implanted ultrasonic sensor that directly measures the blood flow within a patient's circulatory system by the attachment of the sensor onto a blood vessel.
U.S. Pat. No. 5,423,747 (Amano) describes an ultrasonic sensor and an extracorporeal blood pump being used simultaneously to inform a doctor or clinician of any problems or events experienced by a patient. These events may include significant reductions in blood flow from over-pumping the ventricle by the pump or clotting of the blood. When an event is detected, the doctor or clinician may immediately take action to remedy the problem by slowing the pumping speed set-point or stopping the blood pump. This arrangement has several significant disadvantages. The first disadvantage is that the arrangement requires the blood pump and ultrasonic sensor to be extracorporeal relative to the patient, which generally means the patient is bed ridden and restricted to a hospital environment. The second disadvantage is that the described ultrasonic sensor and blood pump are separate components and are not part of an integrated system. In addition, the arrangement described has a relatively large surface area of blood contacting regions which may increase the risk of thrombogenesis or clotting. The third problem is that the described system does not include an automatic control system using the measurements from the ultrasonic transducer to allow a pump controller to automatically adjust the pumping speed set-point of the blood pump without the doctor or clinician manually adjusting the speed, therefore the described system relies entirely on the doctor or clinician detecting a problem and taking immediate action to remedy said problem.
The present invention aims to or at least address or ameliorate one or more of the disadvantages associated with the above mentioned prior art.